Looks like a random event then. I don't know if the siren hangs around and can be caught by patrols, or whether it was a one-off event. Looks like the reverse event to the one where a peasant finds a wounded siren and it ends up on your side.

what lingchih said, but only if oceania is in the game you're playing, if so it is almost certainly siren, and can be on land, now just patrol it can't be too hard to find a bird with a voluptous chest area and a human head - especially when it sings so loud.

I don't know about the oceania thing Nike. I've had Sirens pop as random commanders in many games with different nations. And I have never played Oceania. It might need a water nation to spawn them though.

I don't know about the oceania thing Nike. I've had Sirens pop as random commanders in many games with different nations. And I have never played Oceania. It might need a water nation to spawn them though.

I've seen land nations get Sirens quite often.

It could be a Siren that some other nation got, that is now used to kill your commanders. That sounds more probable than independent Siren knowing to hide and lure.